1. Field of the Invention
The invention relates to new photoresists, particularly photoresists that can be applied and imaged as thick coating layers. Preferred resists of the invention are chemically-amplified positive-acting resists that contain one or more photoacid generator compounds and a resin component.
2. Background
Photoresists are photosensitive films used for transfer of images to a substrate. A coating layer of a photoresist is formed on a substrate and the photoresist layer is then exposed through a photomask to a source of activating radiation. The photomask has areas that are opaque to activating radiation and other areas that are transparent to activating radiation. Exposure to activating radiation provides a photoinduced chemical transformation of the photoresist coating to thereby transfer the pattern of the photomask to the photoresist-coated substrate. Following exposure, the photoresist is developed to provide a relief image that permits selective processing of a substrate.
A photoresist can be either positive-acting or negative-acting. For most negative-acting photoresists, those coating layer portions that are exposed to activating radiation polymerize or crosslink in a reaction between a photoactive compound and polymerizable reagents of the photoresist composition. Consequently, the exposed coating portions are rendered less soluble in a developer solution than unexposed portions. For a positive-acting photoresist, exposed portions are rendered more soluble in a developer solution while areas not exposed remain comparatively less developer soluble. Photoresist compositions are described in Deforest, Photoresist Materials and Processes, McGraw Hill Book Company, New York, ch. 2, 1975 and by Moreau, Semiconductor Lithography, Principles, Practices and Materials, Plenum Press, New York, ch. 2 and 4. While currently available photoresists are suitable for many applications, current resists also can exhibit significant shortcomings, particularly in high performance applications such as formation of highly resolved sub-half micron and sub-quarter micron features.
Consequently, interest has increased in photoresists that can be photoimaged with short wavelength radiation, including exposure radiation of about 300 nm or less, or even about 200 nm or less, such as wavelengths of about 248 nm or 193 nm. Use of such short exposure wavelengths can potentially enable formation of smaller features.
It thus would be desirable to have new photoresists and methods for processing photoresists to enable formation of smaller, highly resolved features. It would be particularly desirable to have such photoresists that could be processed at short wavelengths such as sub-300 nm, especially 248 nm.
We have now found new methods and compositions that enable application and processing of photoresist as thick coating layers, e.g. at dried layer (post soft-bake) thicknesses of in excess of 1 micron, in excess of about 1.5, 2, 3, 4 or even 5 microns.
Resists can be imaged at short wavelengths in accordance with the invention, including 248 nm, to provide highly resolved thick layer relief images. See, for instance, the results set forth in the examples which follow.
In a first aspect, a resist is applied to a substrate as a thick coating layer, e.g. a thickness of from a range of about 1.5 to 5 microns, imaged to patterned activating radiation, and then thermally treated (post-exposure bake or xe2x80x9cPEBxe2x80x9d) at a relatively low temperature, particularly at a temperature that is at least about 10xc2x0 C., 15xc2x0 C., 20xc2x0 C., or 25xc2x0 C. less than standard post-exposure bake processing of current chemically-amplified positive resists. In particular, in the methods of the invention resists are suitably post-exposure baked at a temperature of about 105xc2x0 C. or 100xc2x0 C., more typically about 95xc2x0 C. or 90xc2x0 C.
We have surprisingly found that such mild post-exposure bake treatment can provide highly resolved relief images of the thick coating layers upon development. In contrast, the same or comparable resists coated as thinner layers (e.g. 0.5 microns or less) provide relief images of significantly reduced resolution upon such mild PEB treatment.
Also preferred is where the pre-exposure soft-bake (solvent carrier removal) is conducted at a maximum temperature of at least about 15xc2x0 C. or 20xc2x0 C. greater than the subsequent post-exposure thermal treatment, more preferably the pre-exposure soft-bake is conducted at a maximum temperature of at least about 25xc2x0 C. or 30xc2x0 C. more than the maximum temperature of a subsequent post-exposure thermal treatment. Generally preferred is where is the maximum temperature of the pre-exposure soft-bake is conducted at a temperature of from about 15xc2x0 C. to 35xc2x0 C., particularly about 25xc2x0 C. more than the maximum temperature of the subsequent post-exposure thermal treatment. References herein to a maximum temperature of a thermal treatment (e.g. i) pre-exposure bake or ii) post-exposure, pre-development bake) refers to the maximum temperature reached and retained (e.g. retained for at least about 5, 10 or 15 seconds) during the specified thermal treatment.
In additional aspects of the invention, resist compositions are provided that can facilitate and enhance the deposited thick film coating layer. In particular, resists of the invention may suitably contain a plasticizer compound or composition to promote formation of a thick coating layer.
The resin component also may contain polymers that have a low glass transition temperature, e.g. polymers that have a molecular weight (Mw) of about 30,000 or 20,000 or less, or a molecular weight (Mw) 10,000 or less or 5,000 or less.
The photoacid generator component also may generate relatively large photoacids, e.g. a photoacid having a volume of at least about 155 or 160 xc3x853, more preferably a volume of at least 170, 180 or 190 xc3x853. Even larger photoacids will be suitable, including photoacids having a volume of at least about 200, 220, 250, 280 or 300 xc3x853. Such large photoacids will be less prone to undesired diffusion through a thick resist coating layer.
Particularly preferred photoresists for use in the methods of the invention comprise a polymer having phenolic groups. Even more preferred are photoresists that comprise polymers that have polymerized phenolic units and acrylate units with acid labile groups such as polymerized tert-butyl acrylate, tert-butyl methacrylate, methyladmantyl acrylate, methyladamantyl methacrylate, and the like. Such polymers may be higher order polymers (e.g. terpolymers, tetrapolymers and the like) and contain additional repeat units beyond phenolic units and photoacid-labile alkyl acrylate units. For instance, preferred additional units are relatively inert units such as polymerized styrene or alpha-methylstyrene units. References herein to acrylates are inclusive of substituted acrylates such as methacrylates.
The invention further comprises articles of manufacture comprising substrates such as a microelectronic wafer having coated thereon the photoresists and relief images of the invention. The invention also includes methods to manufacture microelectronic wafers and other articles. Other aspects of the invention are disclosed infra.